Federal and state environmental laws have established limits on the amount of hydrocarbons that an internal combustion engine for certain vehicles may emit into the atmosphere. To meet these limits, a variety of devices and methods has been developed to measure and control the hydrocarbon emissions from the engine of the vehicle. The engine's air induction system has been observed as a source of hydrocarbons released from the engine to the atmosphere. Accordingly, many of the methods and systems employed to measure and control hydrocarbon emissions are directed to the engine's air induction system and exhaust system.
Hydrocarbons are known to evaporate from the interior of the engine and escape into the atmosphere through the engine's air induction system. The evaporative release of hydrocarbons through the air induction system primarily occurs when the engine is not operating. One method of reducing hydrocarbon emissions through the engine's air induction system is to adsorb or trap hydrocarbons with the use of a filter-like device. Typically, the hydrocarbon-trapping device is disposed in the air induction system, and includes an adsorbent material that adsorbs the hydrocarbons, thus substantially preventing the hydrocarbons from escaping into the atmosphere. When the engine is subsequently caused to operate, air flowing through the air induction system into the engine typically is caused to pass through the hydrocarbon-trapping device. The air passing through the hydrocarbon-trapping device purges the device of the adsorbed hydrocarbons. The purging restores the effectiveness of the hydrocarbon-trapping device for adsorbing hydrocarbons during a subsequent period when the engine is not in operation.
One problem that has plagued engine designers has been in respect of the positioning of the hydrocarbon-trapping device in the air induction system. The position and design of the hydrocarbon-trapping device must minimize an interference and therefore a restriction with the flow of fluid through the air induction system and simultaneously provide for the purging of adsorbed hydrocarbons from the hydrocarbon-trapping device during periods when the engine is in operation.
The prior art has typically provided two distinct solutions to these conflicting operational goals. One solution has been to provide a hydrocarbon-trapping device that occupies the entire cross-section of the flow path of the air induction system. U.S. Pat. No. 7,056,474 to Dumas et al. is illustrative of such a solution. This solution provides effective purging of adsorbed hydrocarbons but interferes with fluid flow through the air induction system during the operation of the engine, which reduces the efficiency and/or power output of the engine.
The alternate solution typically employed is to locate the hydrocarbon-trapping device where it does not substantially interfere with the fluid flow through the main flow path of the air induction system. This solution includes disposing the hydrocarbon-trapping device in a superfluous compartment added to the air induction system, or disposing the hydrocarbon-trapping device as a lining on least a portion of an interior surface of the air induction system. U.S. Pat. Nos. 6,997,977 and 7,182,802 disclose such devices. The problems with these solutions are the separate compartment in the air induction system increases a cost thereof and occupies additional space within an engine compartment of the vehicle; the lining of the air induction system increases a cost thereof; and the purging of hydrocarbons during the operation of the engine is reduced which can cause the trap to become saturated with hydrocarbons significantly reducing its efficiency.
It would be desirable to produce an air induction system for an internal combustion engine including a hydrocarbon-trapping assembly that minimizes an interference with a fluid flow through the air induction system while facilitating a purging of hydrocarbons adsorbed thereby during periods when the engine is in operation.